Add check to reduce CESM log output for imp_sol

### Issue Type

Code Clean-up

### Issue Description

Per a post in the CESM forum - https://bb.cgd.ucar.edu/cesm/threads/size-of-cesm-log-file-grows-to-several-gbs.11449/

the imp_sol convergence messages are being printed for every task. Checks for masterproc should be added to avoid this (and thus all messages will be printed to only the atm log)

@fvitt - is this something you might be able to include in an upcoming PR?

### Will this change answers?

No

### Will you be implementing this yourself?

Any CAM SE can do this